1. Field of the Invention
This invention relates to a method of making an optical component to which an optical fiber can be readily attached in proper axial alignment. More specifically, it relates to a method of attaching a fiber alignment ferrule to an expanded beam lens.
Although the present invention also finds utility in devices which couple light from a source to an optical fiber, the present discussion concerning connector alignment problems will be limited to fiber-to-fiber connectors. The butt connection between the ends of two fibers results in an insertion loss that is caused by various optical fiber misalignment parameters, examples of which are as follows: (a) lateral misalignment between the axes of the two fibers, (b) longitudinal misalignment between the endfaces of the two fibers, and (c) angular misalignment between the axes of the two fibers.
The simplest approach to fiber coupling is the butted end coupler in which fibers which have had their endfaces prepared are brought into angular, lateral and axial alignment. Such alignment is difficult to achieve outside the laboratory. Since the butted fiber arrangement is particularly sensitive to lateral displacement, this type of connector is difficult to use in field applications.
Beam expanders employing lenses or tapered fibers have been employed in in-line single-mode fiber connectors which, due to the small core diameter of such fibers, are extremely sensitive to lateral misalignment. Although such beam expanders exhibit a reduced sensitivity to lateral displacement, they are generally very sensitive to angular misalignment. Thus, various alignment mechanisms have been employed for the purpose of angularly aligning a fiber along the optical axis of the beam expanding optical element.
2. Description of the Prior Art
Disclosed in U.S. Pat. No. 4,531,810 (Carlsen) is a plastic optical connector body part having a lens molded in one end thereof and at the opposite end a cylindrical cavity which is centered on the optical axis. An elastomeric fiber holder or ferrule fits within the cavity and frictionally engages the wall thereof. The ferrule has an axial hole for supporting the optical fiber. A fiber is inserted into the ferrule hole so that the end thereof contacts the body part opposite the lens. If the ferrule hole were concentric with the outer cylindrical surface thereof, light radiating from the fiber would be collimated by the lens into a beam which propagates along the optical axis of the connector. However, when a fiber is positioned adjacent the connector body part in the manner described in the Carlsen patent, the fiber endface often deviates from the optical axis of the lens, and/or there is angular misalignment between the fiber axis and the lens optical axis.
U.S. Pat. No. 4,290,667 (Chown) discloses a method of actively aligning a capillary tube ferrule to a plastic lens. A lens body part is formed with a small diameter cavity at one end for receiving a lens and a coaxial, larger diameter hole at the other end. A glass capillary tube, mounted in a chuck of a micropositioner arrangement, is inserted into the large diameter cavity until it abuts the rear surface of the lens. A droplet of refractive index matching cement is placed between the capillary tube and the lens. An optical fiber is inserted down the bore of the chuck so that the end thereof enters the capillary tube. A beam of collimated light from a laser located on the optical axis of the lens is focused to a point near the fiber end. The micropositioner is employed to adjust the axial and longitudinal position of the fiber end to obtain maximum light transmission as indicated by a detector disposed at the remote end of the fiber. The joint is held steady until the cement has set. This method of aligning the capillary tube is time consuming and expensive.